1. Field of the Invention
This invention relates to techniques for improving the dynamic range of analog detectors and, more particularly, to employing a digital interface circuit to improve the dynamic range of an analog energy detector having a random offset which can be hundreds of times greater than the signal produced by a quantum particle.
2. Description of the Related Art
In employing wide dynamic range analog detector arrays for detecting patterns of energy impinging thereon, direct sensing of detector outputs conventionally requires analog multiplex circuity to sample the individual detectors in the array. This analog multiplex circuitry has limited dynamic range, and often introduces Johnson noise and switching noise. The dynamic range of this analog multiplex circuitry is usually significantly lower than the dynamic range of the detectors being sensed and, consequently, limits system dynamic range. Introduction of amplifiers ahead of the multiplex circuitry improves performance, but the full dynamic range of the detector-amplifier combination is still not available because of multiplexer noise.
One-dimensional and two-dimensional image detector arrays have been developed using photodiode technology, charge injection device technology, and charge coupled device technology. The signals produced by the detectors in these arrays are delivered to one or more output nodes using some type of analog multiplexer, usually comprised of either switches or charge transfer devices. The limit on system performance imposed by the multiplexer is a result of the capacitance load of the multiplexer circuitry, Johnson noise introduced by the sampling function, switching interference, or, in the case of charge transfer, the introduction of charge transfer losses and charge transfer noise.
In accordance with aforementioned co-pending application Ser. No. 07/939,333, the dynamic range of an analog sensor is improved by using a digital interface unit with square root companding to reduce the noise produced by analog multiplexing circuitry. The resulting sensor system, however, is not appropriate for configurations in which the detector has a random offset that can be hundreds of times greater than the signal amplitude produced by a quantum particle (an X-ray photon).